I'm just beginning to get back into serious photography after a very long time away. I've toyed with digital, but this is my first foray into trying to do controlled creative work in the digital format.

I'm not certain if the original capture equipment matters much, but I'm currently shooting with a Nikon D3100, and several pieces of Nikon Glass.

For processing right now, I'm working with Lightroom 4.

From what I've read, due to the filters located on the sensor, all RAW files could stand some level of sharpening in post processing. Please correct me if I'm wrong here.

While I understand that the exact amount of sharpening that is appropriate will depend on the image itself...Is there some rule of thumb that can be used as a starting point, particularly when batching a large number of similar raw files? I suppose a follow-up would be, DOES the camera used to capture the image affect that recommendation in any significant way?

Let me know if there is any additional information I can give to help answer.

In Lightroom 4, hold down Option (Mac) or Alt (Windows) as you change the sliders and you'll see the effect it has more clearly. I use opt-slide for Sharpening Mask and Radius all the time, you'll be able to dial in what you want very quickly this way.
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camflanSep 10 '12 at 23:31

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@dpollitt: Equipment used does often matter. The same image photographed with a low density sensor vs. a high density sensor would affect what sharpening settings you apply...the low density sensor will pack more pixels on subject, potentially making pixel-level detail smaller than subject-level detail. You can generally (and sometimes must) use a larger sharpening radius in that scenario. There are a LOT of factors that affect sharpening, however output format is one of the primary ones.
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jrista♦Sep 11 '12 at 0:29

Unfortunately, every image really is different when it comes to sharpening. Here's how I do it when I'm going down the sliders in Lightroom:

Start with setting Amount at 50 or maybe 100. It needs to be above 0 or else there's no sharpening at all and you can't see what the other sliders are doing. It almost certainly won't stay here; you'll come back to this.

Radius depends strongly on the type of detail in the image. Lots of fine details, go with smaller values. If there's not a lot of fine details, you can go higher. You can also use Detail to suppress the effects of Radius and Amount on fine details.

I start Detail at 50. At that level it won't be suppressing the fine details halo very much and you can judge what Amount is really doing. Lower values reduce the effects of Amount and Radius on fine details, while higher values apply more sharpening to fine details.

Set Masking as high as you possibly can so that the sharpening is only affecting edges you want (hold Alt/Option while dragging to see the mask). Remember that affected areas are white, so you want white edges.

With the radius, detail, and masking set, adjust Amount according to your taste.

Basically, you don't want to over-sharpen at this point, and you don't want the sharpening halos around close-proximity edges smashing into each other and ruining the effect.

If you have an area with a lot of fine detail where the edges are competing with each other, first try reducing Detail, then Radius until they're no longer conflicting.

You'll come back to everything again after you apply noise reduction. It never stops!

This is just a starting point – every image is different and you might have a workflow or look that you prefer.

Beyond that, you can also get into creative sharpening (you're probably going to want Photoshop for its layer and blending controls for that) and output sharpening (which Lightroom handles pretty well). For a little more on those, see Patrick Levoie's guide to digital sharpening (.pdf). For lots more details, I'd also recommend the book Real World Image Sharpening by Bruce Frasier and Jeff Schewe.

The specific settings you specify are highly dependent on the pixel density of the sensor, how strong its low pass filter is, and the size of the smallest elements of detail in the scene. It is extremely difficult to provide a "standard" formula for sharpening for any photograph. The more "sub-detail level" noise is, the larger your sharpening radius generally needs to be, however pixel sizes range from around 7 microns to under 4 microns these days, a very LARGE range given the size of details projected by a lens on the the sensor. On my 7D, with 4.3 micron pixels, I often take radius over 2!
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jrista♦Sep 10 '12 at 22:20

Rather than offer any kind of specific settings, its better to offer procedures for identifying the ideal settings to use, allowing readers to apply that procedure to any photo and achieve good results. By offering specific settings, even if you call them starting settings, your readers will have widely differing results, and even varying results for each of their photos if they happen to come from different cameras.
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jrista♦Sep 10 '12 at 22:21

I understand your point, but with Lightroom there actually are some specific values to know. For example, Amount must be above 0 for any of the other sliders to do anything, and Details has almost no effect when set to 100 (counter-intuitively). I've edited my response to be a little more vague, but the OP did ask for some rules of thumb and I've provided mine.
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unexplainedBacnSep 10 '12 at 23:19

Sure, the Amount slider must be above zero, however thats a functional issue, and doesn't really apply in general. Details most definitely as an effect, even up to 100. Details also has a variety of side effects that one should be aware of, such as "sparkle"...which appears in smooth areas with moderate to high noise...and it is extremely difficult to get rid of. Radius, as well as the "Detail" slider for luminance noise removal, also have a very specific and sometimes significant effect, often depending on the ratio of pixels per minimum detail size....
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jrista♦Sep 10 '12 at 23:42

..., however they too have to have their own side effects. I use Lightroom 4.1 myself, and I've spent a considerable amount of time working with both sharpening and noise reduction. I've sharpened photos of subjects that occupied a mere 1/6th the frame, requiring considerable cropping which in turn required considerable sharpening and NR, as well as subjects that occupied 50%, 75%, even 80-90% of the frame. Similar subjects, however they often require radically different sharpening and NR adjustments. I've also used cameras with different pixel sizes, which again has an impact on settings.
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jrista♦Sep 10 '12 at 23:44

For an image to be displayed on the screen, 100% for amount and 1.4 px for radius. View at 100% when making adjustments.

For a 5x7 print at 300 dpi, 200% for amount; 8x10, 300%.

For standard prints (i.e. not canvas), judge the amount of sharpening by looking at the image at 50%. That will get you in the ballpark. If you're looking at a file destined to print output at 100% on the monitor, it should look over sharpened.

Depending on the subject, you might need to mask what's being sharpened. Grass and some foliage doesn't take well to the sharpening.

Image sharpening is a very subjective matter. It is very dependent on a myriad of factors, including output factors (medium size, resolution) as well as camera factors (sensor size, sensor pixel pitch, low pass filter strength, sensor noise level), etc. Even your subject magnification and the size of the finest element of detail in-frame relative to the spatial resolution of the sensor can matter. These factors will all affect how much sharpening you "need", as well as how much sharpening you may "want", relative to an original unsharpened image. Some sharpening might need to be "intrinsic", providing a base degree of sharpness to your image in general, while other sharpening may be "targeted" to a given output...and if you have multiple outputs (i.e. computer screen and print at multiple sizes), then each output will probably need its own unique sharpening tuned for the output medium.

There are no hard and fast rules about what makes for good sharpening and what doesn't. When sharpening for screen, you can often get away with minimal sharpening, or even none at all. The more your subject fills the frame, the less likely you'll need any sharpening. The smaller your output target relative to the native image size, the less likely you'll need sharpening. When you need to crop more, or when your output target is closer to the native image size, you might need more sharpening. The relative resolutions of output medium and working medium also play a role. Print, for example, tends to utilize considerably higher pixel densities than computer screens, by a factor of 3x at a minimum (when using a 100ppi screen) to more than 6x (when using a 72ppi screen or printing at very high resolution, such as 600ppi). When sharpening for print, you can usually apply much stronger sharpening settings with a larger radius than you can when sharpening for screen.

The size of subject detail relative to the size of a pixel can also affect how you sharpen. This can change for the same subject depending on how large the subject is relative to the frame, pixel density of the sensor, and even the resolving capability of your lens. If you use a high quality lens and fill the frame with your subject (whatever it may be, even a landscape taken with a narrow aperture or T/S lens to maximize DOF), you will probably find that you need much less sharpening than if you are using lens of lower quality. When your subject fills a fraction of the frame, you will often need more sharpening to bring out what little detail there may be. That offers the first tip to sharpening....make sure you can fill the frame with your subject (allowing for the artistic addition of negative space where necessary), and avoid the need to sharpen at all.

Another key factor to sharpening, and the ability of sharpening to have an appropriate impact, is image noise. The more noise in your image, the more likely you will enhance noise (rather than detail) with "default" or "canned" sharpening settings. If you have no option but to use a high ISO setting that results in high noise, even if you can fill the frame with your subject, you will probably find you need to use different settings (such as a larger sharpening radius) than when you use a lower ISO setting or have less noise. In the same grain as enhancing noise, sharpening has the tendency to add "halos" around edges and key objects. The stronger the sharpening applied, the stronger the halos will be. The only way to avoid this is to produce a sharper image in camera.

There are no general rules for sharpening. All the technical stuff above aside, ultimately how much sharpening you apply really boils down to your personal aesthetic taste. To some people, a given photo might need sharpening, where as to others, the exact same photo might seem perfectly sharp strait out of the camera. There are also a variety of ways to improve perceived sharpness. The standard sharpening tools of Lightroom are not the only way. The "Clarity" tool, which affects microcontrast, is an alternative or complementary way of improving sharpness without actually needing to apply a high degree of standard sharpening, mitigating the potential impact of haloing while achieving stronger results. There are also a variety of high- and low-pass filtering methods to sharpen photos in a tool like Photoshop which offer different results that may be more appropriate to different subjects.

Sharpening is really a matter of taste, so its best to experiment for a while and find out what works for you. Make it a part of your style.

Things are worse than you imagine. Not only is there no ideal sharpening for an image taken by a specific camera and lens combination, with lens set to a specific aperture, the correct sharpening depends on the output medium and the viewer or photographer's taste. Sharpening is therefore as subjective as anything can be. So the answer is sharpen to taste according to what you see in the final output medium at the desired size.